As China prepares for a generational power shift in the next two weeks, a similar shift is happening online that is testing the limits and displaying the evolution of China's legions of state-directed censors.

Since its launch three years ago, Weibo, China's version of Twitter,
has become the country's water cooler, a place where nearly 300 million Internet users opine on everything from Korean soap operas to China's latest political intrigue.

It has posed a unique challenge for Chinese Communist Party leaders whose overarching goal is to maintain tight political and social control, while at the same time wanting to give their citizens a conduit to blow off steam.

"One of the key challenges for the new leadership will be whether they can establish credibility through new governing mechanisms," said Tony Saich, a professor of international affairs at Harvard Kennedy School in Massachusetts.

"How are they going to deal with a wired, globally connected, urban middle class that is probably less likely over time to be treated like children?"

Part of the solution is also the problem: Weibo.

Last Friday, senior officials from China's Jiangxi province triggered an avalanche of online criticism when they showed up hours late for a commercial flight from Guangzhou. The other passengers were convinced the plane was delayed simply to accommodate the officials, and they were furious.

Government censors let the online anger flow, and the incident was typical of the Weibo exposes that have often revealed details of low level officials' wealth, corruption or abuse of power.

Yet that same day, the New York Times ran a lengthy article on Premier Wen Jiabao family's wealth, which lit up Twitter internationally but hardly made it on to Weibo. All references to the article, direct and obscure, were quickly blocked.

By letting certain types of party criticism flourish on Weibo and even become "trending topics" while censoring even obscure references to others, Chinese authorities have tried to create an illusion of a rowdy online public square.

"Everything going on online, including Weibo, is not happening randomly. It is very much part of a plan," said a China-based American who goes by the alias Martin Johnson. Johnson founded Greatfire.org and Freeweibo.com, websites that monitor China Internet censorship.

"The reason why Weibo exists is because the party allowed it to. The party thinks it can use Weibo to its advantage."

Clocking the watch

A microblogger who goes by the name Huazong has become the so called "watch watchdog" on Weibo. Since July 2011, he has collected photos of officials who wear expensive wristwatches despite earning relatively modest government salaries and posted them online.

Huazong's latest victim is a safety official from the northern Shaanxi province, Yang Dacai, who was removed from his position in September after Weibo users dug up photos and counted more than 10 luxury watches sitting on his wrist on different occasions.

"Some officials have asked why I am doing this and I tell them it is to promote the establishment of an officials' property declaration system," he said.

The freedom Weibo users have to excavate dirt on provincial and county-level officials stands in stark contrast to the muzzle they wear when wanting to discuss the nation's top leaders, whose names, nicknames and weird permutations of their names are blocked on the website.

"In China you can criticise and conduct investigative reports on officials who are lower than the county level, but you cannot criticise the top leaders," said Zhang Zhian, a journalism professor Guangzhou's Sun Yat-sen University.

Part of the reason for the dichotomy is rooted in the geography of power in China: edicts on what to censor are issued from the central government in Beijing. This means provincial officials have less say over what gets cut from China's boisterous Weibo.

"If a party secretary is criticized, it is hard for them to go all the way to Beijing and say 'please delete everything on Weibo about me'," said Xiao Qiang, an adjunct professor at UC Berkeley who founded news website China Digital Times that keeps an updated list of banned words on Weibo.

"If it is just local and does not implicate someone higher up...(the censors) often will let it go. On the other hand, they do make very swift judgments on information they see as challenging the legitimacy of the party," Xiao said.

The censorship, most analysts say, doesn't appear to bother the average Weibo user very much. Industry data has shown that the majority of users on the platform use it for entertainment and not for political or social activism.

"Do I think the Chinese are turned off by the censorship on Weibo? No," said Michael Clendenin, founder of technology consultancy RedTech Advisors. "The average Chinese person is not naive. They know what is happening and choose to participate."

Are you ready for sparta?

Even though discussion of top political leaders and the taboo Ts - Tiananmen, Taiwan and Tibet - are removed from Weibo, debate about political issues exists in code on the platform, making China's Internet freer than before.

While references to the once-in-a-decade political transition, which begins on November 8, are strictly monitored, Internet surfers trying to elude government censors use code words, like "sparta", which has become shorthand for the upcoming Party Congress. Sparta in Mandarin, "si ba da", sounds like the colloquial reference to the 18th party congress, "shi ba da", which is censored on Weibo.

"My Internet speed is becoming slower and slower, is this because of the approaching 'sparta' or is it the end of the world," said one Weibo user. It is common for Beijing to increase Internet monitoring in the lead-up to marquee political events, experts said, often causing Internet speeds to slow significantly.

The continuous cat-and-mouse game, some Internet industry executives say, is actually vital to the stability and development of China, because it gives the Communist Party real-time feedback on policies and a method to take stock of the public mood.

"Social media cannot be said to be 'tightly controlled'," said one high-level Chinese Internet executive, who declined to be named due to the sensitivity of the topic. "It is infinitely more open than the Internet, which is infinitely more open than print media. 'Tightly controlled' may be used only if you are comparing against democratic countries."

When a significantly freer Internet in China will come about is anyone's guess, but most industry experts interviewed expect some loosening after the Party Congress.

That loosening, should it come, will be for an overtly political reason, analysts believe: at the outset of its tenure, the new leadership may want to project an image of being more open to political reform, including freer speech, than the old guard.

Weibo users, in turn, are certain to quickly test just how much freedom the new leadership is willing to tolerate.